The initiation of polymerization by the use of compounds which can be broken down into free radicals is well known in the polymer art. The triazene of the present invention is 3,3-(1,1'-biphenyl-2,2'-diyl)-1-(4-methylphenyl)-1-triazene, the formula of which is: ##STR1##
The advantage of the present compound is believed to be that upon decomposition of this particular triazene two free radicals are formed. The free radicals formed add to monomers produce another radical. Such radical regeneration is characteristic of chain reactions. The radicals formed in the initiation step may then add additional monomer molecules resulting in chain growth or propagation. The chain would continue to grow if it were not terminated in some way which often takes place by a combination or coupling of the growing radical chains.
The general sequence of polymerization by a free radical mechanism is initiation in which the free radical precursor decomposes to form one or more free radicals. The free radicals then attach themselves to the monomers. In a series of steps called propagation the monomers activated by free radicals can attach themselves to other monomers. The propagation may proceed by several monomer radicals continuing to attach themselves one to the other until at some point the sequence is terminated by the completion of a chain without a recurrence of a free radical attachment or active site. This usually occurs by the combination or coupling of the growing radical chains.
The kinetic chain length is directly proportional to monomer concentration squared and inversely proportional to the radical concentration or polymerization rate. An increase in polymerization rate or radical concentration will produce smaller polymer molecules. The kinetic chain length is more a characteristic of a particular monomer and does not depend completely on the method of initiation.